Loan Portfolio and Credit Quality Loans by Portfolio Segment (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 6,893,158	$ 6,505,028
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,074,708	939,690
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	623,037	520,992
Commercial tax-exempt
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	451,671	418,698
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,395,692	2,440,220
Construction and land
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	240,306	164,990
Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,948,973	2,682,533
Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	90,421	99,958
Consumer and other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 143,058	$ 177,637